The present invention relates to optical telecommunication techniques. More particularly, the present invention provides a compact integrated coherent transceiver based on silicon photonics platform, a method for forming the same, and a system having the same.
Over the last few decades, the use of communication networks exploded. In the early days Internet, popular applications were limited to emails, bulletin board, and mostly informational and text-based web page surfing, and the amount of data transferred was usually relatively small. Today, Internet and mobile applications demand a huge amount of bandwidth for transferring photo, video, music, and other multimedia files. For example, a social network like Facebook processes more than 500 TB of data daily. With such high demands on data and data transfer, existing data communication systems need to be improved to address these needs.
40-Gbit/s and then 100-Gbit/s data rates wide-band DWDM (Dense Wavelength Division Multiplexed) optical transmission over existing single-mode fiber is a target for the next generation of fiber-optic communication networks. Chip-scale widely-tunable lasers have been of interest for many applications such as wide-band DWDM communication and wavelength-steered light detection and ranging (LIDAR) sensing. More recently, optical components are being integrated on silicon (Si) substrates for fabricating large-scale photonic integrated circuits that co-exist with micro-electronic chips. a whole range of photonic components, including filters, (de)multiplexers, splitters, modulators, and photodetectors, have been demonstrated, mostly in the silicon-on-insulator (SOI) platform. The SOI platform is especially suited for standard DWDM communication bands at 1300 nm and 1550 nm, as silicon (n=3.48) and its oxide SiO2 (n=1.44) are both transparent, and form high-index contrast, high-confinement waveguides ideally suited for medium to high-integration planar integrated circuits (PICs).
Coherent optical fiber communications were studied extensively in the 1980s mainly because high sensitivity of coherent receivers could elongate the unrepeated transmission distance; however, their research and development have been interrupted for nearly 20 years behind the rapid progress in high-capacity wavelength-division multiplexed (WDM) systems using erbium-doped fiber amplifiers (EDFAs). Not long ago, the demonstration of digital carrier phase estimation in coherent receivers has stimulated a widespread interest in coherent optical communications again. The fact is, the digital coherent receiver enables us to employ a variety of spectrally efficient modulation formats such as M-ary phase shift keying (PSK) and quadrature amplitude modulation (QAM) without relying upon a rather complicated optical phase-locked loop. In addition, since the phase information is preserved after detection, we can realize electrical post-processing functions such as compensation for chromatic dispersion and polarization-mode dispersion in the digital domain. These advantages of the coherent receiver have enormous potential for innovating existing optical communication systems.
Coherent transmitter has a TE and TM path. Silicon photonics chip, however, operates essentially only in a TE only configuration. Several technical challenges exist for making polarization-independent or wavelength tunable passive and active components as well as integrating these components to form a coherent optical transceiver in a compact silicon photonics platform. Therefore, improved techniques and methods of forming an integrated compact coherent transceiver are desired.